The statements in this background section merely provide background information related to the present disclosure and may not constitute prior art.
Engineers typically design high-pressure plunger pumps useful in oilfield operations in two sections; a (proximal) power section and a (distal) fluid section. The power section typically comprises a crankshaft, reduction gears, bearings, connecting rods, crossheads, crosshead extension rods, etc. Common fluid sections usually comprise a plunger pump housing (a.k.a. block) having a suction valve in a suction bore, a discharge valve in a discharge bore, a plunger in a plunger bore, and an access bore, as well as high-pressure seals, gaskets, retainers, and ancillary hardware.
Valve terminology can vary according to the industry (e.g., pipeline or oil field service) in which a valve is used. In some applications, the term “valve” means just the moving element or valve body. In the present application, the term “valve” may be used in a general sense as appropriate for the context and can include components other than the valve body, e.g., various valve guides, valve seats, and/or one or more valve springs and/or valve inserts (seals).
In FIG. 1 there is shown a cross-sectional schematic view of a typical fluid section of a plunger pump showing its connection to a power section by stay rods. A plurality of fluid sections similar to that illustrated in FIG. 1 may be combined, as suggested in the Triplex fluid section housing schematically illustrated in FIG. 2, such pumps having multiple fluid sections being well-known.
Each individual bore in a plunger pump housing is subject to fatigue due to alternating high and low pressures which occur with each stroke of the plunger cycle. Conventional plunger pump housings frequently fail due to fatigue cracks in one or more areas defined by the intersecting suction, plunger, access and discharge bores, as illustrated in FIG. 3. Towards reduction of fatigue cracking in high pressure plunger pump housings described above, Y-block housing designs exemplified by that shown schematically illustrated in FIG. 4A have been proposed. The Y-block design reduces stress concentrations in a plunger pump housing such as those shown in FIGS. 1 and 3 by increasing the angles of bore intersections above 90°. In the example illustrated in FIG. 4A, the bore intersection angles are approximately 120°. A more complete cross-sectional view of a Y-block plunger pump fluid section is schematically illustrated in FIG. 4B.
Although several variations of the Y-block design have been evaluated, few, if any, have become commercially successful for several reasons. One reason is that mechanics find field maintenance on Y-block fluid sections difficult. For example, replacement of plungers and/or plunger packing is significantly more complicated in Y-block designs than in the earlier designs represented by FIG. 1. In the earlier designs, provision is made to push the plunger distally through the plunger bore and out through an access bore (see, e.g., FIG. 3). This operation, which would leave the plunger packing easily accessible from the proximal end of the plunger bore, is not possible in a Y-block design. Thus, a Y-block configuration, while reducing stress in plunger pump housings relative to earlier designs, is associated with significant disadvantages, such as cracks as shown in FIG. 4A.
Advances in high pressure plunger pump housings that provide both improved internal access and superior stress reduction are expressed in U.S. Pat. Nos. 6,623,259, 6,544,012 and 6,382,940, which are incorporated herein by reference. One embodiment of a right angular plunger pump such as that described in U.S. Pat. No. 6,623,259 (the '259 patent) is schematically illustrated in FIG. 5. It includes a right-angular plunger pump housing 12 comprising a suction bore 3, discharge bore 5, plunger bore 7, and access bore 9. Suction bore 3 and discharge bore 5 are each internally fitted with a valve that permits fluid flow in one direction only, such that when plunger 11 is withdrawn from housing 12 during normal pump operation, a reduced pressure zone is created substantially in the center of housing 12, enabling ambient pressure to cause suction valve 13 to open, thus admitting a fluid that is desired to be pumped to enter the interior of housing 12. Once a material that is desired to be pumped is present within housing 12 and plunger 11 is moved into housing 12 following its withdrawal during an operation cycle, pressure created by such action causes suction valve 13 to close upon its seat 15 whilst simultaneously causing discharge valve 17 to be moved from discharge valve seat 19, enabling material flow through discharge bore 5 and out of housing 12, during such normal operation of a plunger pump. The suction bore 3 and discharge bore 5 each include a portion having substantially-circular cross-sections for accommodating, e.g., a valve seat. Suction and discharge bores 3, 5 that accommodate valve seats 15, 19 are sometimes slightly conically-shaped to facilitate the secure and substantial leak-proof fitment of each valve seat within a bore of pump housing 12 (e.g., by press-fitting a valve seat that has an interference fit with the pump housing). Less commonly, the portions of suction and discharge bores intended to accommodate a valve seat are cylindrical instead of being slightly conical. Further, each bore (i.e., suction, discharge, access and plunger bores) comprises a transition area which interfaces with other bore transition areas.
The plunger bore 7 of the right-angular plunger pump housing of FIG. 5 comprises a plunger bore having a proximal packing area (i.e., an area relatively nearer the power section) and a distal transition area (i.e., an area relatively more distant from the power section). Between the packing and transition areas is a right circular cylindrical area for accommodating a plunger. The transition area of the plunger bore facilitates interfaces with analogous transition areas of other bores as noted above.
Each bore transition area of the right-angular pump housing of FIG. 5 has a stress-reducing feature comprising an elongated (e.g., elliptical or oblong) cross-section that is substantially perpendicular to each respective bore's longitudinal axis. Intersections of the bore transition areas are typically chamfered, the chamfers comprising additional stress-reducing features. Further, the long axis of each such elongated cross-section is substantially perpendicular to a plane that contains, or is parallel to, the longitudinal axes of the suction, discharge, access and plunger bores.
An elongated suction bore transition area, as described in the '259 patent, can simplify certain plunger pump housing structural features needed for installation of a suction valve. Specifically, the valve spring retainer of a suction valve installed in such a plunger pump housing does not require a retainer arm projecting from the housing. Nor do threads have to be cut in the housing to position the retainer that secures the suction valve seat. Benefits arising from the absence of a suction valve spring retainer arm include stress reduction in the plunger pump housing and simplified machining requirements. Further, the absence of threads associated with a suction valve seat retainer in the suction bore eliminates the stress-concentrating effects that would otherwise be associated with such threads, as shown in the Y-block of FIG. 4B, which denotes the high stress concentrations in the threads.
Threads can be eliminated from the suction bore if the suction valve seat is inserted via the access bore and the suction bore transition area and press-fit into place as described in the '259 patent. Following this, the suction valve body can also be inserted via the access bore and the suction bore transition area. Finally, a valve spring is inserted via the access bore and the suction bore transition area and held in place by a similarly-inserted oblong suction valve spring retainer, an example of which is described in the '259 patent. The '259 patent illustrates an oblong suction valve spring retainer having a guide hole (for a top-stem-guided valve body), as well as an oblong suction valve spring retainer without a guide hole (for a crow-foot-guided valve body). Both of these oblong suction valve spring retainer embodiments are secured in a pump housing of the '259 patent by clamping about an oblong lip, the lip being a structural feature of the housing (see FIG. 5 for a schematic illustration of oblong lip 266 in a right angular plunger pump housing).
The '259 patent also teaches means for mounting discharge valves in the fluid end of a high-pressure pump incorporating positive displacement pistons or plungers. For well service applications both suction and discharge valves typically incorporate a traditional full open seat design with each valve body having integral crow-foot guides. This design has been adapted for the high pressures and repetitive impact loading of the valve body and valve seat that are seen in well service. However, stem-guided valves with full open seats could also be considered for well service because they offer better flow characteristics than traditional crow-foot-guided valves. But in a full open seat configuration stem-guided valves may have guide stems on both sides of the valve body (i.e., “top” and “lower” guide stems) or only on one side of the valve body (e.g., as in top stem guided valves) to maintain proper alignment of the valve body with the valve seat during opening and closing. Conventional valve designs incorporating secure placement of guides for both top and lower valve guide stems have been associated with complex components and difficult maintenance. U.S. Pat. Nos. 6,910,871 and 7,513,759 describe alternative methods and apparati related to valve stem guide and spring retainer assemblies and to plunger pump housings in which they are used. Such plunger pump housings can incorporate one or more of the stress-relief structural features described herein, plus one or more additional structural features associated with use of alternative valve stem guide and spring retainer assemblies in the housings. Such plunger pump housings do not, however, comprise an oblong lip (see, e.g., structure 266 in FIG. 5 as noted above) for securing a suction valve spring retainer. The absence of this oblong lip simplifies machining of the plunger pump housing, and the corresponding design results in reduced stress within the pump housing.
Available seats for plunger-type pumps used in hydraulic fracturing of sub-strata have been standardized by manufacturers and fracturing pump users to promote commonality, increase availability, and reduce costs of these highly expendable components. Standard high-pressure seat designs commonly used in the industry feature seats with a shoulder and a seat taper of 0.75 inches per foot on the diameter. This taper mates with a similar taper in the fluid end. This very “fast” taper is insufficient to retain the seat in a locked position and when the seat is subjected to very high valve loads. Due to such a fast taper, a shoulder is necessary on the seat to prevent the seat from sliding down the taper when the seat is subjected to very high valve loads. Thus, the seat shoulder is exposed to very high downward or axial loads, which results in the very high stresses in the fillet, as further discussed herein. Some pumps designed by Halliburton Inc. feature a taper of 1.5 inches per foot on the diameter of one or more of the bores. While the seats for the Halliburton pumps have no shoulder and the outside taper is continuous, the fluid ends for Halliburton pumps include a shoulder at the very bottom of the bore taper for the purpose of preventing the seat from sliding down the taper. This shoulder results in very high stresses at the fillet at the corner of the fluid end taper and bottom shoulder.